Arg. Saesneg gwreiddiol = Original English ed.: Harlow: Longman Group, 1994.
Cer i'w nôl e, Harri Parri! by Sheila Lavelle. ISBN 1860850324. Published by Uned Iaith Genedlaethol Cymru CBAC in 1996. Publication and catalogue information, links to buy online and reader comments.